Seven Arm Octopus: also known as the blob octopus or sometimes called septopus, is one of the two largest known species of octopus. The seven-arm octopus is so named because in males, a specially modified arm used in egg fertilization is coiled in a sac beneath the right eye. Due to this species' thick, gelatinous tissue, the arm is easily overlooked, giving the appearance of just seven arms.